Piezoresistive pressure sensors are, as a rule, made up of a sensor element (or sensor die) having a membrane. On this membrane there are situated for example four stress-sensitive piezoresistors connected to form an electrical bridge circuit.
When there is a temperature gradient over the sensor element, this means that the piezoresistors have different resistance values due to the different temperatures. This can cause a change in the electrical bridge voltage, due to a temperature gradient, that cannot be distinguished from a change in the electrical bridge voltage due to an applied pressure. Even a few millikelvins can cause a deviation in the electrical bridge voltage that corresponds to a few pascals of pressure change.